The present invention relates to a charge and discharge control circuit controlling charge and discharge of a secondary cell by ON/OFF of a switch circuit.
A charge and discharge control circuit has been disclosed in the prior art, in which a switch circuit is connected to a secondary cell in series and the switch circuit is controlled by ON/OFF control to control charge and discharge of the secondary cell thereby. For example, in controlling charge and discharge of a lithium ion cell, whether the terminal voltage of the lithium ion cell is more than the predetermined level is detected comparing voltage by a comparator. When it is detected that the terminal voltage is more than the predetermined level, the switch element of the switch circuit is turned OFF so as to stop charge. The above construction is introduced in general. As the result, overcharge state is surely detected and charge to the secondary cell is controlled so that the secondary cell does not become the overcharge state not responding the transient change of cell voltage. Although control to stop current supply from the secondary cell to the load detecting overdischarge and control to stop current supply from the secondary cell to the load detecting overcurrent are carried out similarly in the charge and discharge control circuit, the delay circuit are used respectively by the similar reason in those controls.
Therefore, in the prior charge and discharge control circuit like this, it needs to form a delay circuit respectively in each of the overcharge detecting circuit, overdischarge detecting circuit, and overcurrent detecting circuit, and a capacitor for setting delay time is formed respectively in three delay circuits. In this manner, as the capacitor for setting delay time on each control is needed at each delay circuit, the charge and discharge control circuit causes increase cost thereof and has a problem to increase the mounting area.
An object of the present invention therefore is to solve these problems in the prior art and to provide a charge and discharge control circuit obtaining required delay time at each control using one capacitor in common.